<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
</head>
<body>
    <input type="button" value="点击" id="btn">

    <script src="../js/common.js"></script>
    <script>
        var btn = getId('btn');
        // btn.addEventListener('click', function() {
        //     alert('Hello');
        // }, false);  //IE9以后支持  common.js里去解决兼容性

        addEventListener(btn, 'click', function() {
            alert('Hello');
        })
        addEventListener(btn, 'click', function() {  //对btn进行第二次事件注册
            alert('World！');
        })
    </script>
</body>
</html>